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Tropical Atlantic Cooling And African Deforestation Correlate To Drought

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  • Pat Neuman
    Tropical Atlantic Cooling And African Deforestation Correlate To Drought Santa Barbara CA (SPX) Dec 02, 2005 Against the backdrop of the Montreal Summit on
    Message 1 of 1 , Dec 4, 2005
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      Tropical Atlantic Cooling And African Deforestation Correlate To

      Santa Barbara CA (SPX) Dec 02, 2005
      Against the backdrop of the Montreal Summit on global climate being
      held this week, an article on African droughts and monsoons, by a
      University of California, Santa Barbara scientist and others, which
      appears in the December issue of the journal Geology, underlines
      concern about the effects of global climate change.

      Tropical ocean temperatures and land vegetation have an important
      effect on African monsoon systems, explains first author Syee
      Weldeab, a post-doctoral fellow in the Department of Earth Science
      at the University of California, Santa Barbara. The monsoons are
      critical to sustaining agriculture in equatorial Africa.

      Weldeab says that man's reduction of inland vegetation cover through
      deforestation and overgrazing in equatorial Africa and increases in
      global temperatures through the emission of greenhouse gases will
      likely strongly affect the African monsoon system in the future.

      "The weakening of the monsoon has a huge effect," says
      Weldeab, "resulting in shortages of harvests and hunger."

      As vegetation is cleared, the land loses its capacity to retain heat
      and becomes cooler. As the land cools relative to the ocean, there
      is a larger gradient between the ocean temperature and the land
      causing less moisture to be pulled from the ocean air toward the

      Weldeab and his colleagues studied cores from beneath the ocean
      floor of the Gulf of Guinea, in the tropical Atlantic just off the
      coast of Cameroon, to understand the history of climate in the area
      for the past 10,000 years. The cores contain foraminifera, tiny
      plankton shells that are composed of calcium and trace elements. By
      studying the ratios of magnesium and calcium in the shells, the
      scientists are able to correlate that information to past
      temperature changes in the ocean. In analyzing these records for the
      past 10,000 years, the scientists found three pronounced cooling
      periods which indicate drought.

      Besides the ocean records, the scientists analyzed data from four
      lakes that are distributed across central Africa on the monsoon
      belt. The three sea surface cooling periods found by the scientists
      correlate to records of low lake levels. These clearly were times of
      drought; the land became more arid.

      The authors state, "periods of drought likely brought about
      environmental hardship, triggering population migration, giving rise
      to changes in the modes of agricultural production, and influencing
      the fall or rise of civilizations."

      Weldeab points out that the past 50 years are marked by
      deforestation and overgrazing much greater than that of the past,
      thus disturbing the climate system that results from the coupling of
      sea surface temperature and vegetation cover on land.

      "We can't predict how, but it is clear that this human-induced
      change will change the terrestrial and ocean system," he says. He
      notes that droughts in this region are currently occurring more
      frequently than in the past few thousand years, although the
      frequency of the droughts is unpredictable.

      "People in less developed countries live from rain, harvests and
      animal husbandry," says Weldeab. "Drought directly affects them;
      they run out of food for people and animals."

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